This invention relates to guiding means in rock drilling for guiding a percussion drill string comprising a guide sleeve which is rotatable relative to the drill string and adapted to follow axially therewith during drilling. Specifically, the invention relates to a guide sleeve and a drill rod adapted to be used in the guiding means.
In rock drilling by means of a percussion drill string comprising a plurality of consecutive drill rods the drill bit has normally a larger diameter than the coupling sleeves, which interconnect the drill rods, thereby allowing the cuttings to be flushed out of the drill hole and the drill rods to be rotated. Due to this fact there is a risk that the drill string is bent with the result that the pursued straightness of the hole is not achieved. For purposes of improving this straightness it has been proposed to use particular guide sleeves, which have a larger diameter than conventional coupling sleeves and which are provided with longitudinally extending ridges for allowing by-pass of the cuttings. A guide sleeve of this type is shown in U.S. Pat. No. 3,136,377. Those prior art guide sleeves are intended to rotate together with the drill string in normal operation. However, in case any hindrances to the rotation of the guide sleeve should occur during drilling, the drilling operation can still be continued, since the drill string may rotate independent of the guide sleeve. In practice, however, it has been found that the ridges of the guide sleeve do cause such large friction against the wall of the drill hole that the rotation of the drill string is made more difficult, and large wear is caused on the guide sleeve at its end faces.
U.S. Pat. No. 2,072,320 suggests to use roller bearings between the guide sleeve and the drill string in a drill string for rotary drilling. This is an expensive solution which furthermore is unsuitable in percussive drilling.
The object of the invention is to provide improved guiding means for guiding percussion drill strings, which does not have the above-mentioned disadvantages.
Another object of the invention is to design the guide sleeve and a drill rod carrying same in such a way that a simplified assembling of the guide sleeve is obtained.
The above and other purposes are attained by giving the invention the characterizing features state in the appending claims.